Power lines brought down Alfred ‘Skip’ Nichols’ rig, killing 16 people in Texas in July

The pilot of a hot-air balloon that crashed in Texas in July had drugs in his system—including the chemicals found in codeine, sedatives, Ritalin and antidepressants—at the time of the accident, according to a National Transportation Safety Board investigation.

Alfred ‘Skip’ Nichols was piloting the balloon when it struck high-voltage power...